Photo-electric tube



June 11, 1935. FJSCHROTER ET AL 2,004,176

PHOTO ELECTRIC TUBE Filed D60. 11, 1931 lNVENTgrR' FRITZ SCHR ER OTTO SCHNE I A ORNEY Patented June 11, 1935 UNITED STATES 2,004,176 PHOTO-ELECTRIC TUBE Fritz Schriiter and Otto Schriever, Berlin, Germany, assignors to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. H., Berlin, Ger i many, a corporation of Germany Application December 11, 1931, Serial No. 589,252 In Germany Decemberll, 1930 4 Claims. (Cl. 250-275) It is known that the current output of a photo-. electric tube may be increased by introducing in it an inert gas under low pressure. The primary electrons releasedby the light from the photo 5 active material generate in the gas filled space new electrons by virtue of impact ionization, and the number of the new electrons increases markedly with increasing velocity of the primary electrons, i. e., with increase in anode potential applied to the tube. The increase in the photoelectric current thereby insured is limited because the acceleratingpotential applied to the tube cannot be raised beyond a certain value or limit at which there begins an unassisted glow discharge which is no longer subject to control by the, light. The present invention has the purpose of providing a photo-tube wherein the anode potential applied to the tube, and thus the velocity of the electrons may be raised to very high values without causing initiation of the unassisted glow discharge.

With this end in view, according to the invention, the process of electron acceleration and that of impact ionization are caused and occur in two distant spaces or chambers which are separated from each other by a diaphragm which while practically gas tight, permits a large portion of the high-speed electrons to pass through it.

The principle of the invention is illustrated in the examples shown in the accompanying drawmg: in which Figure ,l is a longitudinal section of one form of tube constructed in accordance with the invention; Fig. 2 is a plan view of the F diaphragm of the tube shown in Fig. 1; and Fig. 30 3 is a longitudinal section of a modified form of tube embodying the invention.

The tube shown in Fig. l, to illustrate in principle the construction of a tube embodying the in vention, comprises a sealed glass envelope l divided into two chambers 2 and 3 which are separated from each other by an electron permeable diaphragm or partition, such as a thin metal foil 5. The partition or foil may be reinforced and its 45 mechanical strength increased by a grating or wire netting 6 adjoining it or placed on it as shown in Figure 2. v The chamber 2 is exhausted of air as far as feasible, and contains a photoelectric cathode 4 with reference to which the metal partition or foil 5 has a positive potential high enough to impart to the electrons issuing from the photoelectric cathode under the action of light a high acceleration or velocity by virtue of which most of them will be caused to pass thru the metal foil and thus enter the chamber 3 which is filled with rarefied gas. The chamber 3 contains two electrodes l and 8' insulated from each other and which, for instance, as shown in the illustration, may consist of two helically wound wires interleaved with each other. The 5 electrons passing thru the metal foil or partition cause intense ionization of the gas in the chamber 3 owing to their high'speed. A suitably high potential difference is maintained between the electrodes 1 and 8 to cause a current to flow be- 10 tween them as a secondary effect of the illumination, and this current, which is dependent on the illumination, exceeds by far the current producible in photoelectric tube known in the prior art.

Another form of two chamber photoelectric l5 tube somewhat more suitable for practical purposes is shown in Figure 3. The electrons given ofi by the photo responsive cathode 4 in high vacuo first reach the metallic foil 5, which is positively charged with reference to the cathode; in 2 cidentally the electrons experience a consider able acceleration, and thus for the most part pass thru the foil 5 and enter the gas filled ionization chamber '3, which has a metal wall 9 and a pin type electrode Ill located in the axis 5 thereof, and the ionic current produced as a secondary action will flow between them. In

order to prevent part of the electrons released at the'photo-responsive electrode from reaching the outeside of the ionizing chamber instead of 39 hitting the permeable metal foil, an apertured. metallic shield II which may optionally be connected with the said-"photoelectric cathode, is provided as shown in the drawing.

The potential applied between the light responsive cathode 4 and the metal foil 5 of the ionizing chamber neednot necessarily be direct; indeed,

"in some practical cases it may be of greater advantage to apply between them an alternating potential whenever the photoelectric tube currents are to be further amplified, and the alternating potential may be used as a carrier wave for the light variations. In this case it will be found of advantage to keep the metal Wall 9 of the ionizing chamber .at ground potential in order that the alternating potential may be dependably shielded from the secondary circuit.

In order to minimize inertia the ionizing chamber should preferably be filled with hydrogen or argon or a mixture of these two gases.

In case the metal foil disposed between the two chambers should not be sufliciently gas tight in the course of time, it may be found advisable to preserve or restore the high vacuum inside the 55 cathode chamber by the use of a gas absorbent or getter.

Having now described our invention, what we claim and desire to secure by Letters Patent is the following:

1. A photo tube comprising a sealed envelope, a gas tight metal diaphragm permeable to high speed electrons and mounted in said envelope dividing it into two separate gas tight chambers, one of said chambers being highly evacuated and having a light transparent wall and the other chamber containing gas at low pressure, a photoelectric cathode mounted in said highly evacuated chamber, and a pair of cooperating electrodes mounted in the other chamber.

2. A photo tube comprising a sealed envelope, an electron permeable gas tight partition mounted in said envelope dividing it into two gas tight chambers, one highly evacuated and the other filled with gas at low pressure, a photoelectric cathode in said highly evacuated chamber, a tuloular electrode mounted in said gas filled chainloer with its open end in registry with said partition, and a pin electrode mounted coaxially or and insulated from said tubular electrode to form one electrode of a discharge gap to said light intensity upon the photosensitive electrodes.

tuloular electrode. 3. A photo tube comprising a sealed envelope, a gas tight metal diaphragm permeable to high speed electrons supported withinthe envelope and dividing it into two separate gas tight chamhere, one of the chambers being highly evacuated and having'a light transparent wall and the other chamber containing gas at low pressure, a light sensitive electrode element positioned in the highly evacuated portion of the envelope, a pair of cooperating electrodes located in the other portion of the envelope, and a,

shield between the photosensitive member and the diaphragm to confine the photoactive electron stream in its path so that substantially all N emitted electrons pass through the diaphragm.

k. A light sensitive device comprising a sealedenvelope, an electron permeable gas tight mem-- her supported within the envelope and divid-' ing it into a plurality of independent gas tight chambers, an angularly disposed photosensitive electrode positioned in one chamber to he responsive to light rays directed angularly toward the envelope, and a plurality of electrode elements supported in a second chamber within the envelope to produce, upon the penetration or the gas tight member by the light emitted electrons, a magnified current output of a value proportional to the current producilole by a given r'ar'rz somerset. orro sormmvna. 

